Process for the recovery of metal chlorides from jarosite sludges resulting from the sulphuric acid processing of ores

Abstract

In a process for the recovery of metal chlorides from jarosite in sludges which result from the sulphuric acid processing of ores, the sludge is treated with an aqueous solution of an alkaline earth metal chloride. This solution contains free hydrochloric acid and is in excess stoichiometric ratio to the sulphate content of the sludge. The insoluble materials are separated from the metallic chloride solution by filtering, and are stripped of metallic chlorides by washing and further filtering. The metallic chloride solutions are then collected. The alkaline earth chloride is preferably calcium chloride. The process is particularly, but not exclusively, applicable to recovering metals from jarosite-type sludge resulting from the processing of zinc ore.

I claim: 
     
       1. A process for use in recovering valuable metal chlorides from jarosite sludges resulting from sulphuric acid processing of ores comprising a. contacting the sludge with an aqueous solution of an alkaline earth metal chloride which contains free hydrochloric acid and is in excess stoichiometric ratio to the sulphate content of said sludge so as to dissolve said contained metals in chloride form and precipitate sulphate ions in the form of an alkaline earth metal sulphate;   b. separating insoluble products including said alkaline earth metal sulphate from the metallic chlorides solution resulting from step (a) by filtration;   c. stripping said separated insoluble products of metallic chlorides by washing and filtration; and   d. recovering metallic chloride solutions from steps (b) and (c).   
     
     
       2. A process as set forth in claim 1, wherein said alkaline earth metal chloride is calcium chloride. 
     
     
       3. A process as set forth in claim 1, wherein said alkaline earth metal chloride solution is formed in situ by mixing hydrochloric acid and a calcium compound containing an anion which is displaceable by the hydrochloric anion. 
     
     
       4. A process as set forth in claim 3, wherein said calcium compound is calcium hydroxide or calcium carbonate. 
     
     
       5. A process as set forth in claim 1, wherein said free acid in said treatment solution is hydrochloric acid at a concentration of between 3N and 9N. 
     
     
       6. A process as set forth in claim 5, for recovering metal chlorides from basic sulphate sludges resulting from the processing of zinc ore, wherein said treatment solution comprises, per kilogram of dry sludge, substantially 1 kilogram of calcium chloride, substantially 1 liter of 9N hydrochloric acid, and substantially 1.75 liters of water, the treatment lasting substantially 75 minutes at substantially 105° C. 
     
     
       7. A process as set forth in claim 1, wherein the treatment solution used in step (a) contains an amount of free hydrochloric acid such that the pH of the solution at the end of the treatment of step (a) is less than the pH at which precipitation of hydroxides of said contained metals occurs. 
     
     
       8. A process for use in recovering valuable metal chlorides from sludges of jarosite type resulting from the sulphuric acid processing of zinc ores, comprising a. contacting the sludge at a temperature close to the boiling point with an aqueous solution of alkaline earth metal chloride which contains free hydrochloric acid and is in excess stoichiometric ratio to the sulphate content of said sludge, so as to dissolve said contained metals in chloride form and precipitate sulphate ions in the form of an alkaline earth metal sulphate;   b. separating insoluble products including said alkaline earth metal sulphate from metallic chloride solution resulting from step (a) by hot filtration;   c. stripping said insoluble products of metallic chlorides by hot washing and filtration; and   d. recovering the metallic chloride solution resulting from steps (b) and (c).   
     
     
       9. A process as set forth in claim 8, wherein said free hydrochloric acid is at concentration of between 3N and 9N.